The accumulation of excess triglyceride in the liver is known as hepatic steatosis (or fatty liver), and is associated with adverse metabolic consequences, including insulin resistance and dyslipidemia. Fatty liver is frequently found in people who intake excessive alcohols and who have obesity, diabetes, or hyperlipidemia. Nonalcoholic fatty liver disease (NAFLD) refers to a wide spectrum of liver disease ranging from simple fatty liver (steatosis), to nonalcoholic steatohepatitis (NASH), to cirrhosis (irreversible, advanced scarring of the liver). All of the stages of NAFLD have in common the accumulation of fat (fatty infiltration) in the liver cells (hepatocytes), and NAFLD is now the leading cause of chronic liver disease in the United States.
The NAFLD spectrum is thought to begin with and progress from its simplest stage, called simple fatty liver (steatosis). Simple fatty liver involves the accumulation of fat (triglyceride) in the liver cells with no inflammation (hepatitis) or scarring (fibrosis). The next stage and degree of severity in the NAFLD spectrum is NASH, which involves the accumulation of fat in the liver cells, as well as inflammation of the liver. The inflammatory cells can destroy liver cells (hepatocellular necrosis), and NASH can ultimately lead to scarring of the liver (fibrosis), followed by irreversible, advanced scarring (cirrhosis). Cirrhosis that is caused by NASH is the last and most severe stage in the NAFLD spectrum.
In 2008, a genomewide association study of individuals with proton magnetic resonance spectroscopy of the liver to evaluate hepatic fat content, a significant association was identified between hepatic fat content and the Patatin-like Phospholipase Domain Containing 3 (PNPLA3) gene (see, for example, Romeo et al. (2008) Nat. Genet., 40(12):1461-1465). Studies with knock-in mice have demonstrated that expression of a sequence polymorphism (rs738409, I148M) in PNPLA3 causes NAFLD, and that the accumulation of catalytically inactive PNPLA3 on the surfaces of lipid droplets is associated with the accumulation of triglycerides in the liver (Smagris et al. (2015) Hepatology, 61:108-118). Specifically, the PNPLA3 I148M variant may promote the development of fibrogenesis by activating the hedgehog (Hh) signaling pathway, leading to the activation and proflieration of hepatic stellate cells and excessive generation and deposition of extracellular matrix (Chen et al. (2015) World J. Gastroenterol., 21(3):794-802).
Currently, treatments for NAFLD are directed towards weight loss and treatment of any secondary conditions, such as insulin resistance or dyslipidemia. To date, no pharmacologic treatments for NAFLD have been approved. Therefore, there is a need for therapies for subjects suffering from NAFLD.